Lawler, J.J. and N.H. Schumaker. 2004. Evaluating habitat as a
surrogate for population viability using a spatially explicit
population model. Environ. Mont. Assess. 94:85-100. WED 04-001

Because data for conservation planning are always limited,
surrogates are often substituted for intractable measurements such
as species richness or population viability. We examined the ability
of habitat quality to act as a surrogate for population performance
for both Red-shouldered Hawks (Buteo lineatus) and Northern
Goshawks (Accipiter gentiles). We compared simple measures of
habitat quality to estimates of population growth rates obtained
from a spatially explicit model of population dynamics. We found
that habitat quality was a relatively poor predictor of simulated
population growth rates for several reasons. First, a relatively
small proportion of the potential habitat for each species served as
population sources in our simulations —15% for Red-shouldered Hawks
and 2% for Goshawks. Second, when habitat quality correctly
predicted demographic sources on the landscape, it consistently
underestimated the contribution of these areas to the population. In
areas where habitat quality correctly anticipated the presence of
demographic sinks, we found no useful quantitative relationship
between the two measures. Our simulation model captured the
influence of habitat quality on the hawk populations, but it also
incorporated interactions between dispersing individuals and
landscape patterns. Thus, the discrepancies we observed likely
reflected the influence of forest fragmentation and the spatial
arrangement of forest patches on the populations. We conclude that
simple measures of habitat quality will often be poor surrogates for
population persistence, but that spatially explicit population
models can help inform the development of better indices.